The most dynamic segment of orthopedic and neurosurgical medical practice over the past decade has been spinal devices designed to fuse the spine to treat a broad range of degenerative spinal disorders. Back pain is a significant clinical problem and the annual costs to treat it, both surgically and medically, is estimated to be over $2 billion. Motion preserving devices to treat back and extremity pain have, however, created a treatment alternative to fusion for degenerative disc-disease. These devices offer the possibility of eliminating the long term clinical consequences of fusing the spine that is associated with accelerated degenerative changes at adjacent disc levels.
While total disc replacement is seen as a major advance over fusion, the procedure to implant the devices in the lumbar spine requires a major operation via an anterior approach, subjecting patients to the risk of significant complications. These include dislodgement of the device, which may damage the great vessels, and significant scarring as a consequence of the surgical procedure itself, which makes revision surgery difficult and potentially dangerous. Thus, there are advantages to spinal implants that can be inserted from a posterior approach, a technique with which spine surgeons are much more experienced. The posterior surgical approach also has the benefit of being able to directly address all pathologies that may be impinging the neural elements, which is not possible from an anterior approach. Motion preserving spinal devices that can be implanted with a minimally invasive, posterior procedure offer the benefit of less surgical trauma and faster patient recovery and also offer cost savings to payers with patients staying fewer days in the hospital.
Motion preserving devices placed posteriorly typically either rely on the spinous processes to support the implant or require pedicle screws to be inserted. However, spinous processes are not load bearing structures and are not rigid. In a population of patients with back pain, the laminae offer a much stronger structure to position an implant, since they consist of significantly stronger bone, and the laminae are also closer to the spine's axis of rotation. Pedicle screws have several disadvantages when used as attachments for motion preservation devices. The procedure to implant them is considered major surgery requiring a wide exposure. The screws are also subject to significant loads and screw loosening is a known consequence over time in these cases. Removing the screws and fusing the spine requires major revision surgery.